Study: weeds get unintended 'fitness' boost from genetic modification

Genetically modified (GM) crops could give harmful weeds a
significant growth boost if their modifications are transferred
into the wild.

Rice weeds with a herbicide-resistant genetic modification
produced up to 125 percent more seeds and had photosynthesised at
rates up to 109 percent higher than control plants.

The research from the Fudan University in Shanghai, published in
New Phytologist, suggests that an experimental gene
modification that protects against the widely-used glyphosate
herbicide also confers significant fitness benefits to weeds.

"Originally, this epsps transgene was developed to confer
resistance to glyphosate," write the authors. "But it also appears
to provide profound and previously unrecognised benefits for plant
growth and seed production."

The transfer of genetic modifications into the wild is a thorny
issue, with cases of herbicide-resistant weeds stoking the debate about
whether GM crops should be used or not. This study lends some
credence to fears that certain genetic modifications can have
unintended consequences on other plants, but it should be noted
that the researchers passed the modification to the weeds by
hand and the modification that they passed is not currently
used.

"There's a risk when you have closely-related wild versions,"
says Wendy Harwood of The John Innes Centre. But that's why we take
those risks into account when considering where and how to plant GM
crops, she added.

The genetic modification transferred in this study concerns
epsps, a key enzyme in plants, which permits the production of
vital amino acids and other substances. Decreased levels of epsps
results in the death of a plant. Glyphosate blocks the function of
epsps, making it a powerful and widely-used herbicide.

One-way, therefore, of ensuring that your herbicide kills the
plants you hate -- the weeds -- but leaves alone the plants you
love -- your crops -- is by altering the epsps enzyme so that it
isn't affected by glyphosate. This is done by either changing the
enzyme directly, or by forcing the plant to over-produce epsps, so
that the glyphosate is overwhelmed.

It is this second route, which is not used commercially, that
the Fudan University researchers investigated. By breeding GM and
non-GM weeds from the same lineage, they were able to show that
this genetic modification resulted in "dramatic changes in
fitness-related traits". They were unable to conclusively rule out
the unlikely possibility that other factors, like the placement of
the genes, had caused the changes.

Harwood said that the study was interesting, and that it would
certainly be looked at carefully by other researchers in the field,
but warned against drawing broad conclusions from a single study.
"One report can't be applied to GM generally," she said, noting
that each crop and each genetic modification has to be looked at on
a case by case basis.